1. Field of Invention
The present invention relates to an exhaust port structure of a cylinder head. More particularly, the present invention relates to an exhaust port structure of a cylinder head in which an exhaust manifold is integrally formed to the cylinder head so as to reduce weight and improve efficiency.
2. Description of Related Art
In the case of a diesel engine, an exhaust system may include a cylinder head having a plurality of exhaust ports, an exhaust manifold, and a turbocharger.
In most cases, the exhaust manifold is made from expensive materials such as steel use stainless SUS, and the weight of the exhaust manifold is over 3 kg. Therefore, an exhaust manifold integrated cylinder head in which the exhaust manifold is integrally formed with the exhaust ports is provided so as to reduce the weight of the cylinder head and improve durability.
FIG. 1 is a schematic drawing of a conventional art in which the exhaust manifold is integrally formed with the exhaust ports. As shown in FIG. 1, the conventional art has a problem in that there is a large deviation in the flow coefficients Cf of the exhaust ports because the shape of the exhaust ports 1 and 4 connected to the first cylinder C1 and the fourth cylinder C4 is different from the shape of the exhaust ports 2 and 3 connected to the second cylinder C2 and the third cylinder C3. The flow coefficient Cf is defined as a ratio of a quantity of exhaust gas flowing from a combustion chamber after combustion to a quantity of exhaust gas flowing from the end of an exhaust pipe. A smaller deviation of the exhaust flow coefficient of Cf is better for the exhaust gas recirculation rate (EGR rate) and the turbocharger efficiency (T/C efficiency). However, the deviation is large in the case of the conventional art because the flowing routes of the exhaust ports are different from each other because of the shape and length difference of the exhaust ports, such that the prior art has a problem of deteriorating the exhaust gas recirculation rate (EGR rate) and the turbocharger efficiency (T/C efficiency).
Further, the conventional art has a problem that the probability of a head crack increases significantly when the heat load is increased because of the exhaust gas, since the outlets of the exhaust ports 1, 2, 3, and 4 are so close to each other to make up a bulkhead structure S as shown in FIG. 1.
The structure of the conventional art shown in FIG. 1 is also difficult to apply to a diesel engine which is provided with a turbocharger because an exhaust hole 5 is located between the second cylinder C2 and the third cylinder C3.
In the case of the diesel engine provided with a turbocharger, the turbocharger can be located between the third cylinder C3 and the fourth cylinder C4 because it is more profitable for the diesel engine considering lay-out of the diesel engine and load capacity of the vehicle. But in the case of the conventional art, the exhaust hole 5 is located between the second cylinder C2 and the third cylinder C3 as shown in FIG. 1 such that it is structurally difficult to connect the turbocharger with the exhaust hole 5.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.